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Louisville-based climate group tracks surging summer heat

Organization's numbers for Fort Collins are mirrored by increase in Boulder

By Charlie Brennan

Camera Staff Writer

Posted:
02/08/2014 03:00:00 PM MST

With temperatures in the past week having straddled a numbing 0, let's contemplate a toastier number: 95.

A recent study of extreme heat trends in Fort Collins found that the city experienced three times the average frequency of days 95 degrees or hotter in the past 14 years than it registered in the previous four decades.

A report released last week by the nonprofit, Louisville-based Rocky Mountain Climate Organization showed that from 2000 through 2013, Fort Collins averaged 8.8 days per year of 95-plus days, whereas from 1961 through 1999, the annual average was just 2.9 days.

For days reaching 90 degrees or higher, the change was similarly dramatic. From 1961 through 1999, Fort Collins averaged 17.9 days a year that were that hot. From 2000 through 2013, the frequency nearly doubled, to a yearly average of 33.7 days of 90 or more.

Stephen Saunders, president of the Rocky Mountain Climate Organization, said the trend for Fort Collins would likely be mirrored by Boulder and other Front Range communities, particularly in the northern half of the state.

"I know of no reason why there should be a large-scale difference between Boulder and Fort Collins," said Saunders, noting that this is the first such study done focusing on any single Colorado community. "It is suggestive, certainly, for other parts of the state."

The report also highlighted data linking extreme heat to the state's most destructive wildfires of the past two years.

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The High Park Fire west of Fort Collins in 2012, which destroyed 259 homes and killed one person, started on a day the high in Fort Collins was 93. The Waldo Canyon blaze, claiming 347 homes and two lives, started on a day Colorado Springs touched a record-tying high of 100. And the Black Forest Fire last year north of Colorado Springs, which torched 488 homes and killed two, sparked on a day the city sweltered at 97.

Saunders sees the recent history of heat as bolstering the argument for doing everything possible to reduce greenhouse gas emissions that are widely believed to be contributing to climate change around the globe.

Summer temperature climb 'apt to continue'

"We clearly need to do more at the state level, we clearly need to do more at the national level, and we clearly need to do more at the international level," Saunders said. "Local information on local climate impacts will be crucial in achieving the strong majority support we need to make all that happen, at all those levels."

The analysis done by Saunders' group suggests that with no change to the current climate trends, Fort Collins would be facing 17 days per year of 95 degrees or higher by 2050, and 38 such days each year by the end of the century.

"This an indication that the climate is changing," said Kevin Trenberth, distinguished senior scientist at the National Center for Atmospheric Research in Boulder who focuses on climate variability. "This is part of the larger picture. Why is the climate changing? Certainly, there is a lot of natural variability that occurs, but we understand that the main cause of global warming is human influence.

"These types of trends are apt to continue. We end up with a longer summer, in some sense, and an increased risk of wildfire is a major issue along the Front Range and through the region. Those kinds of threats to our way of life and existence are ones that we need to take seriously."

Boulder numbers show similar trend

State climatologist Nolan Doesken was prompted by the study to take a look at Boulder's corresponding numbers and found that they parallel the increase found in the Fort Collins study.

Doesken's office reported that Boulder averaged 25 days of 90-plus heat each year from 1961 through 1999, but averaged 38 such days per year from 2000 to 2102. For days of 95 degrees or higher, Boulder's annual average was five days from 1961 to through 1999, compared to a yearly average of 12 from 2000 to 2012.

Doesken cautioned that the Fort Collins weather station — which he manages — has seen the immediate environment change around it in its 125-year history, leading to a greater number of buildings and paved walkways and parking areas, which inevitably have some bearing on the observed rise in temperatures.

He also noted that Boulder's official weather station, now situated on the National Institute of Standards and Technology campus on South Broadway, "has changed location and hands many times" over the city's history.

"But the fact is," Doesken said, "based on a really clean data set that we have in Fort Collins, that darn it, we've been sharply hotter in the summer, and the number of hot days have been noticeable since 2000, with only a couple of years that were an exception."

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